A bike covers 40 km with a speed of 20 km/hr. Find the speed of the bike for the next 30 km journey so that the average speed of the whole journey will be 25 km/hr.

Explanation

Let the speed for the next 30 km be x kmph. Average Speed = Total Distance/Total Time e e Total Distance = 40 + 30 = 70 km Total Time = 40/20 + 30/x = (2 + 30/x) hours => 25 = 70/(2 + 30/x) => 50 + 750/x = 70 => 70x – 50x = 750 => 20x = 750 => x = 37.5 kmph